Spinal and medullary reflex components of the somatosympathetic reflex discharges evoked by stimulation of the group IV somatic afferents

Lumbar V3 interneurons provide direct excitatory synaptic input onto thoracic sympathetic preganglionic neurons, linking locomotor, and autonomic spinal systems

Although sympathetic autonomic systems are activated in parallel with locomotion, the neural mechanisms mediating this coordination are incompletely understood. Sympathetic preganglionic neurons (SPNs), primarily located in the intermediate laminae of thoracic and upper lumbar segments (T1-L2), increase activation of tissues and organs that provide homeostatic and metabolic support during movement and exercise. Recent evidence suggests integration between locomotor and autonomic nuclei occurs within the brainstem, initiating both descending locomotor and sympathetic activation commands. However, both locomotor and sympathetic autonomic spinal systems can be activated independent of supraspinal input, in part due to a distributed network involving propriospinal neurons. Whether an intraspinal mechanism exists to coordinate activation of these systems is unknown. We hypothesized that ascending spinal neurons located in the lumbar region provide synaptic input to thoracic SPNs. Here, we demonstrate that synaptic contacts from locomotor-related V3 interneurons (INs) are present in all thoracic laminae. Injection of an anterograde tracer into lumbar segments demonstrated that 8-20% of glutamatergic input onto SPNs originated from lumbar V3 INs and displayed a somatotopographical organization of synaptic input. Whole cell patch clamp recording in SPNs demonstrated prolonged depolarizations or action potentials in response to optical activation of either lumbar V3 INs in spinal cord preparations or in response to optical activation of V3 terminals in thoracic slice preparations. This work demonstrates a direct intraspinal connection between lumbar locomotor and thoracic sympathetic networks and suggests communication between motor and autonomic systems may be a general function of the spinal cord.

Spinal electrical stimulation to improve sympathetic autonomic functions needed for movement and exercise after spinal cord injury: a scoping clinical review

Spinal cord injury (SCI) results in sensory, motor and autonomic dysfunction. Obesity, cardiovascular and metabolic diseases are highly prevalent after SCI. Although inadequate voluntary activation of skeletal muscle contributes, it is absent or inadequate activation of thoracic spinal sympathetic neural circuitry and sub-optimal activation of homeostatic (cardiovascular, temperature) and metabolic support systems that truly limits exercise capacity, particularly for those with cervical SCI. Thus, when electrical spinal cord stimulation (SCS) studies aimed at improving motor functions began mentioning effects on exercise-related autonomic functions, a potential new area of clinical application appeared. To survey this new area of potential benefit, we performed a systematic scoping review of clinical SCS studies involving these spinally mediated autonomic functions. Nineteen studies were included, 8 used transcutaneous and 11 used epidural SCS. Improvements in BP at rest or in response to orthostatic challenge were investigated most systematically, whereas reports of improved temperature regulation, whole body metabolism and peak exercise performance were mainly anecdotal. Effective stimulation locations and parameters varied between studies, suggesting multiple stimulation parameters and rostrocaudal spinal locations may influence the same sympathetic function. Brainstem and spinal neural mechanisms providing excitatory drive to sympathetic neurons that activate homeostatic and metabolic tissues that provide support for movement and exercise and their integration with locomotor neural circuitry are discussed. A unifying conceptual framework for the integrated neural control of locomotor and sympathetic function is presented which may inform future research needed to take full advantage of SCS for improving these spinally mediated autonomic functions.

Dynamic changes in arterial pressure following high cervical transection in the decerebrate rat

Objective: Spinal transection has variable effects on arterial pressure, with some investigators demonstrating a precipitous decline and others reporting only a minimal decrease below normal. Recovery of arterial pressure following spinalization occurs with varying time courses - in some cases over days and in others over weeks to months. Given these findings, we sought to systematically test the hypothesis that in the unanesthetized decerebrate rat, arterial pressure would recover to pre-transection values over an acute time course.Design: Experiments were performed on a total of six Sprague-Dawley unanesthetized decerebrate adult male rats. In four rats, we determined dynamic changes in arterial pressure and heart rate in response to C₁ transection.Results: Immediately following spinal cord injury, there were significant decreases in systolic blood (SBP) and mean arterial pressure (MAP), but not diastolic blood pressure (DBP). SBP, DBP, and MAP were significantly greater 170 min post-transection compared to immediate and 5 min-post transection values and were not statistically significantly different from pre-transection control. Heart rate decreased significantly following transection, but not immediately following the spinal cord injury. Lung inflation elicited depressor responses in all animals tested (n = 4 animals) and in three animals resulted in bradycardia. Hypercapnia tests effected a decrease in arterial pressure and heart rate (n = 3 animals).Conclusions: We demonstrate that in the unanesthetized decerebrate spinalized animal, arterial pressure is reduced by spinal transection and recovers over an acute time course to pre-transection values.

Spinal genesis of Mayer waves

Variability in cardiovascular spectra was first described by Stephan Hales in 1733. Traube and Hering initially noted respirophasic variation of the arterial pressure waveform in 1865 and Sigmund Mayer noted a lower frequency oscillation of the same in anesthetized rabbits in 1876. Very low frequency oscillations were noted by Barcroft and Nisimaru in 1932, likely representing vasogenic autorhythmicity. While the origins of Traube Hering and very low frequency oscillatory variability in cardiovascular spectra are well described, genesis mechanisms and functional significance of Mayer waves remain in controversy. Various theories have posited baroreflex and central supraspinal mechanisms for genesis of Mayer waves. Several studies have demonstrated the persistence of Mayer waves following high cervical transection, indicating a spinal capacity for genesis of these oscillations. We suggest a general tendency for central sympathetic neurons to oscillate at the Mayer wave frequency, the presence of multiple Mayer wave oscillators throughout the brainstem and spinal cord, and possible contemporaneous genesis by baroreflex and vasomotor mechanisms.

Somato-Visceral Effects in the Treatment of Dysmenorrhea: Neuromuscular Manual Therapy and Standard Pharmacological Treatment

OBJECTIVES

This study aims to verify whether neuromuscular therapy (NMT) or pharmacology therapy (PT) is more effective for reducing symptoms in women affected by primary dysmenorrhea and the effects associated with each treatment.

DESIGN

A controlled, randomized, single-blind clinical trial within the framework of the chair of physical medicine and rehabilitation of the University "G. d'Annunzio" of Chieti-Pescara. The study was conducted on a sample of 60 women suffering from primary dysmenorrhea. Subjects were randomly divided in two groups (A and B). Group A was treated with NMT and group B with PT. Group B was given ibuprofen or naproxen because they are considered the best painkillers for this condition. Group A was treated with 8 neuromuscular manual lumbosacral and abdominal therapy sessions twice per week for 4 weeks. Results were analyzed at the beginning (T0) and end (T1) of the study with a menstrual distress questionnaire, brief pain inventory, and visual analogue scale. Twenty patients from Group A were selected for evaluation of their maintenance of the eventual improvement that was detected in T1 at follow-up (T2).

RESULTS

Both therapies had significant short-term effects in reducing the perception and duration of pain. However, NMT appears to give more improvements in the duration of pain. NMT had a long-term effect on perception of pain because patients conserved the positive effects of treatment after 4 weeks. NMT also had a long-term effect on duration of pain because patients conserved benefits of treatment, but this improvement started to decrease after 4 weeks.

CONCLUSIONS

In the treatment of primary dysmenorrhea, NMT represents a valid therapeutic alternative method to PT. NMT is free from potential adverse effects of analgesics, is noninvasive, and is easy to perform.

Effect of gentle cutaneous stimulation on heat-induced autonomic response and subjective pain intensity in healthy humans

The present study examined whether touch influences the autonomic responses and subjective pain intensity induced by noxious heat stimulation in humans. Heart rate and digital pulse wave were recorded. Heat stimulation was applied to the right plantar foot before, during, and after touch. Subjective pain intensity was evaluated using a visual analog scale (VAS). Touch was applied over the right medial malleolus for 10 min. Two types of touch were employed in a cross-over double-blinded randomized manner. When touch was applied with a soft elastomer brush, heat-induced autonomic responses attenuated significantly, while VAS scores were unchanged. In contrast, touch with a flat disc was ineffective for any measurement. Participants hardly perceived a difference in the texture of the touching materials. The present study result suggests there are mechanisms in conscious humans where some sort of touch inhibits nociceptive transmission into autonomic reflex pathways independent of sensation and cognition.

Asymmetrical changes in lumbar sympathetic nerve activity following stimulation of the sciatic nerve in rat

Noxious stimulation of the leg increases hind limb blood flow (HBF) to the ipsilateral side and decreases to the contralateral in rat. Whether or not this asymmetrical response is due to direct control by sympathetic terminals or mediated by other factors such as local metabolism and hormones remains unclear. The aim of this study was to compare responses in lumbar sympathetic nerve activity, evoked by stimulation of the ipsilateral and contralateral sciatic nerve (SN). We also sought to determine the supraspinal mechanisms involved in the observed responses. In anesthetized and paralyzed rats, intermittent electrical stimulation (1 mA, 0.5 Hz) of the contralateral SN evoked a biphasic sympathoexcitation. Following ipsilateral SN stimulation, the response is preceded by an inhibitory potential with a latency of 50 ms (N=26). Both excitatory and inhibitory potentials are abolished following cervical C1 spinal transection (N=6) or bilateral microinjections of muscimol (N=6) in the rostral ventrolateral medulla (RVLM). This evidence is suggestive that both sympathetic potentials are supraspinally mediated in this nucleus. Blockade of RVLM glutamate receptors by microinjection of kynurenic acid (N=4) selectively abolished the excitatory potential elicited by ipsilateral SN stimulation. This study supports the physiological model that activation of hind limb nociceptors evokes a generalized sympathoexcitation, with the exception of the ipsilateral side where there is a withdrawal of sympathetic tone resulting in an increase in HBF.

Role of unmyelinated fibers in electroacupuncture cardiovascular responses

The afferent fiber type responsible for the transmission of sensory neural traffic to the central nervous system during acupoint stimulation is uncertain. Several early studies evaluating compound action potentials have suggested that myelinated fibers contribute to the afferent input of the autonomic reflex adjustments during electroacupuncture (EA). Our more recent data, employing single unit recordings of somatic afferents, show that both myelinated and unmyelinated fibers are stimulated by EA, although more finely myelinated than unmyelinated fibers are activated by low frequency, low current stimulation. We hypothesized in this study that unmyelinated group VI fibers also contribute significantly to the inhibitory influence of EA on cardiovascular pressor responses. We found that neonatal capsaicin-treated rats depleted of substance P from primary afferents were insensitive to the inhibitory EA effect during gastric distention. Thus, EA at P5-P6 reduced gastric distention-induced pressor responses from 19+/-3 to 11+/-2 mmHg in eight untreated rats while capsaicin-treated rats (n=9) were unresponsive to EA. Substance P containing neurons in dorsal root ganglion cells at Ti-T5 were significantly decreased in the capsaicin-treated rats from 47+/-4 to 22+/-4 cells. Treated compared to untreated rats also demonstrated a significantly (P<0.03) reduced number of group IV fibers identified with single unit recording techniques. This study demonstrates that the inhibitory effect of EA at P5-P6 on cardiovascular autonomic excitatory reflexes involves unmyelinated group IV fibers of the median nerves.

Excitation of baroreceptors depresses A- and C-components of the somato-cardiac sympathetic reflex in anesthetized rats

The effect of baroreceptor activation on somato-cardiac sympathetic reflex discharges was examined in urethane-anesthetized, vagotomized, and artificially ventilated rats. Single shock stimulation of myelinated (A) and unmyelinated (C) fibers in the tibial nerve of the left hindlimb elicited two separate excitatory reflex discharge components in a branch of the cardiac sympathetic nerve. They are termed the A- and C-components of the somato-cardiac sympathetic reflex discharges. When aortic nerves (AN) and carotid sinus nerves (CSN) were intact, a sudden increase in mean arterial blood pressure to about 150 mmHg induced by I.V. injection of phenylephrine (50 micro/kg) depressed the A- and C-components by up to 47 +/- 5.4 and 37 +/- 7.7% of the control values, respectively. However, bilateral sino-aortic denervation completely abolished the pressure-induced depression of both components. We conclude that baroreceptor afferent signals from the AN and CSN inhibit both A- and C-components of the excitatory somato-cardiac sympathetic reflex discharges. This and other previous evidence mentioned in the text indicate that inhibitory cardiac sympathetic reflexes originating from arterial baroreceptors and excitatory ones originating from somatic afferents interact, probably at the brainstem.

Excitatory and inhibitory A- and C-reflexes in pelvic parasympathetic efferent nerves elicited by single shock to A and C afferent fibers of perineal and limb somatic nerves in anesthetized rats

The effects of single electrical shocks to myelinated A and unmyelinated C afferent fibers of perineal and limb somatic nerves on the reflex discharges in pelvic parasympathetic (L6/S1) efferent nerves to the bladder were examined in anesthetized central nervous system (CNS)-intact and acute spinal rats. When the bladder was empty, stimulation of perineal somatic inputs to the L6 and S1 segments from the perineo-femoral branch of a pudendal nerve produced excitatory A- and C-reflex discharge components in postganglionic parasympathetic efferent nerve branches on the bladder surface. When the bladder was expanded and pelvic efferent neurons were rhythmically active, additional inhibitory A- and C-reflex components could be seen. After acute spinal transection, the same stimuli elicited excitatory A- and C-reflex discharges of similar latency as those observed before the spinal transection, but were of larger amplitude and longer duration; resting activity in the pelvic nerve was low, and no evoked inhibitory reflex components could be observed. Electrical stimulation of afferents in the tibial nerve had no effect when the bladder pressure was low, but when the bladder was distended, early and late components of reflex inhibition and excitation of parasympathetic activity were visible in CNS-intact rats; these reflex responses were abolished following spinalization.

Single electrical shock of a somatic afferent nerve elicits A- and C-reflex discharges in gastric vagal efferent nerves in anesthetized rats

The possibility that single electrical shock stimulation of somatic afferent nerves could evoke a reflex response in vagal efferent nerves innervating the stomach was examined using anesthetized, artificially-ventilated rats. A single shock to a hindlimb afferent nerve (tibial nerve) produced two distinct reflex components in gastric vagal efferent nerves; namely (1) A-reflex discharges with a latency of about 120 ms and a duration of about 200 ms elicited by stimulation of myelinated A afferent fibers, and (2) C-reflex discharges with a latency of about 360 ms and a duration of about 200 ms elicited by stimulation of unmyelinated C afferent fibers. A single shock to a first lumbar spinal afferent nerve produced only a week reflex component with a latency of about 120 ms and a duration of about 190 ms in gastric vagal efferent nerves. Limb afferents appear to have stronger central pathways functionally connecting to gastric vagal efferent preganglionic neurons in the brainstem, than do abdominal afferents.

A- and C-reflexes elicited in cardiac sympathetic nerves by single shock to a somatic afferent nerve include spinal and supraspinal components in anesthetized rats

The spinal and supraspinal components of both A- and C-reflexes were studied in the somato-cardiac sympathetic reflex discharges elicited by a single electrical shock either to a spinal (T3-4) afferent nerve or to a limb (tibial) afferent nerve in urethane anesthetized rats. In central nervous system (CNS) intact rats, a single shock to a T3-4 spinal afferent nerve produced early and late A-reflex discharges with latencies of 20 +/- 1 ms and 62 +/- 6 ms, respectively, and a C-reflex with a latency of 136 +/- 9 ms in a cardiac sympathetic efferent nerve. After spinalization at the first cervical level, stimulation of the same spinal afferent nerve produced an A-reflex with the same latency as the early A-reflex in CNS-intact rats and a C-reflex with a latency of 86 +/- 3 ms. The amplitude of the early A-reflex became augmented after spinal transection. On the other hand, a single shock to a tibial afferent nerve evoked an A-reflex discharge with a latency of 41 +/- 2 ms and a C-reflex discharge with a latency of 210 +/- 13 ms in CNS-intact rats. These A- and C-reflexes elicited by stimulation of a tibial afferent nerve were not observed after spinalization. It was concluded that cardiac sympathetic A- and C-reflex discharges evoked by stimulation of a segmental spinal afferent nerve in CNS-intact rats are of spinal and supraspinal origin, and those evoked by tibial nerve stimulation are of supraspinal origin. The spinal reflex pathway is segmentally organized, because the spinal reflex is evoked only when stimulation is delivered to afferent nerves close to the cardiac sympathetic outflow segments. With the CNS intact, the spinal reflex component is depressed by descending inhibitory pathways originating in the brain.

Asymmetry and time-course of cutaneous sympathetic reflex responses following sustained excitation of chemosensitive nociceptors in humans

Sympathetic reflex responses were elicited in human volunteers by sustained selective excitation of nociceptors by noxious chemicals, namely topical application of mustard oil which elicited burning pain, or histamine which induced itching in a skin area of 5 cm2 on the volar aspect of one forearm. Stimulus-related sympathetic reflex responses were studied by means of computer-assisted infrared thermography of the palmar aspects of both hands. Nociceptive stimulation induced a decrease of skin surface temperature in both hands interpreted as vasoconstriction. The magnitude of the reflex cooling was correlated with the magnitude of the sensation (r = 0.49), but independent of the quality of sensation (itch or pain). The temperature reduction was maintained for more than 30 min and its time-course matched the time-courses of pain or itch sensations. It is concluded that the sustained and selective excitation of nociceptors elicits a sustained sympathetic reflex response, which adapts very slowly. The time-course of the reflexes suggests that these are not arousal responses, but may be indicators of nociceptive processing in conscious humans. Contralateral temperature decreases were consistently smaller than ipsilateral ones. Thus, sustained nociceptive-specific vasoconstrictor reflexes may be somatotopically organised with an emphasis on areas close to the painful stimulus (homotopic), which has so far only been shown in animals. The study thus demonstrates for the first time in humans the presence of a sympathetic reflex asymmetry, which is specific for nociceptive afferent input.

Stimulation of saphenous afferent nerve produces vasodilatation of the vasa nervorum via an axon reflex-like mechanism in the sciatic nerve of anesthetized rats

The present study was intended to examine the physiological relevance of peptidergic afferent vasodilative fibers in the regulation of blood flow in the vasa nervorum, with special reference to the axon reflex. The response of nerve blood flow (NBF) in the sciatic nerve to electrical stimulation of saphenous nerve afferents was examined using laser Doppler flowmetry in anesthetized rats whose lumbosacral afferents and efferents had been disconnected from the spinal cord. Repetitive electrical stimulation of unmyelinated fibers in the central cut end of the saphenous nerve produced an increase in NBF in the sciatic nerve ipsilateral to the stimulation, independent of changes in mean arterial blood pressure. This increase was abolished by topical application of a calcitonin gene-related peptide (CGRP) receptor antagonist, hCGRP (8-37). In conclusion, NBF in the sciatic nerve is regulated via an axon reflex-like mechanism by unmyelinated afferent CGRP containing vasodilators with collaterals in the saphenous nerve.

Effect of noxious stimulation on sympathetic vasoconstrictor outflow to human muscles

1. In fifteen healthy volunteers, muscle nerve sympathetic activity (MSA) was recorded from the peroneal nerve using microneurography. Blood pressure and electrocardiogram were also recorded. 2. Painful stimuli, adjusted to the subject's tolerance level, were delivered over 30-60 s via (a) pressure to the nail-bed of different digits, and to the trigeminal region, (b) electrical stimulation (5 Hz) of digital nerves and of the supraorbital nerve, or (c) instillation of soap solution into one eye. Non-painful ocular pressure was also applied. 3. All procedures except electrical stimulation of digital nerves caused a marked increase in MSA (mean, 160-248%) with preserved pulse synchrony and a rise in blood pressure. Stimulation of digits induced tachycardia, whereas stimulation of the trigeminal region tended to cause bradycardia. 4. Despite similar pain ratings, electrical stimulation of digital nerves caused a smaller MSA response than the other stimuli (mean increase, 40%). 5. It is concluded that sustained noxious stimulation in awake humans evokes a generalized MSA increase; the activity is still under baroreflex control, but the inhibitory level is reset. Both spinal and brainstem reflexes may contribute; a defence reaction is an unlikely explanation. It is suggested that the number of afferent C fibres activated by electrical stimulation of digital nerves was insufficient to induce any marked MSA response. 6. The non-painful oculo-cardiac reflex is associated with a strong increase in MSA.

Systemic administration of procaine suppresses the somato-sympathetic reflex discharges in anesthetized cats

Somato-sympathetic reflex discharges (SSRDs) which were induced from the lumbar sympathetic truck elicited by train pulse stimulation of femoral nerves in anesthetized cats were examined during and after intravenous infusion of 1 mg.kg(-1).min(-1) of procaine. The infusion demonstrated that amplitudes were suppressed with prolonged latencies and/or their tendencies in A- and C-reflex potentials of SSRDs. Heart rate and blood pressure decreased slightly, and the decreases correlated with time courses of suppressed SSRDs. These results suggest that the systemic procaine infusion may be a reliable method to alleviate somato-sympathetic reflexes under such conditions as extreme stimulation of somatic afferent nerves observed in surgical procedures.

Muscle chemoreflexes and exercise in humans

This review focuses on the role afferent nerves from the contracting muscles play in linking muscle metabolism to the cardiovascular adjustments during exercise by means of a 'muscle chemoreflex'. In the 1930s Alam and Smirk provided the first clear evidence that human (and animal) skeletal muscles are innervated by chemosensitive afferents that can evoke increases in arterial blood pressure. They proposed that the purpose of the increase in pressure was to improve blood flow to the active muscles. Subsequent studies have identified the slowly conducting group IV afferents as the major class of fibres participating in the sensory arm of this reflex. Most of these fibres travel via the dorsal roots to the ipsilateral spinal cord where they synapse in the substantia gelatinosa and release substance P or other peptide transmitters. The second order (or higher) neurons cross to the contralateral side of the spinal cord and travel rostrally to stimulate brainstem cardiovascular centres and increase arterial pressure. Current evidence favours the concept that substances associated with muscle acidosis provide the stimulus to the afferents. In humans, chemosensitive afferent activation causes a marked increase in vasoconstrictor efferent muscle sympathetic nerve activity. It is unclear if the muscle chemoreflex improves blood flow to 'underperfused' active muscles by augmenting arterial pressure, or if the increase in sympathetic outflow restrains metabolic vasodilatation to regulate arterial blood pressure during activities like running or cycling.

Somatic and vagal afferent convergence on solitary tract neurons in cat: electrophysiological characteristics

Electrophysiological characteristics are described for 67 neurones localized to subnuclei of the solitary tract or the area of the dorsal motor nucleus of the vagus in alpha-chloralose-anesthetized, paralysed cats which received vagal and hindlimb sural or peroneal nerve excitation. The peroneal and sural nerves were stimulated in an exposed hindlimb preparation; the ipsilateral vagus was stimulated at the cervical level. Compound action potentials were recorded from all three nerves. Neurons were recorded with extracellular microelectrodes from the brain stem solitary area contralateral to the stimulated somatic nerves. Ninety-one percent of the recorded neurons were spontaneously active. Eighteen percent and 5% of the neurons received only peroneal or sural excitation, respectively, while 59% of the neurons received convergent peroneal and sural excitation. Thirty-nine of the 67 neurons were also tested for vagal input of which 41% responded with excitation. All of the neurons tested for vagal input also received converging excitation from one or both of the somatic nerves. Thirty-one percent of the vagal-excited neurons received converging input from both the peroneal and sural nerves. The combined mean minimal conduction velocity for peroneal and sural input was 31 +/- 1 m/s (mean +/- 1 S.E., range 9-54 m/s). Thirty-six percent of the peroneal and 31% of the sural afferents were Group II fibers. Significant periods of inhibition of spontaneous neuronal spike activity followed peroneal and sural excitation in 43 and 39% of the neurons, respectively. In many neurons, both excitation and inhibition of spike activity could be elicited at stimulus intensities as low as 1.2 times threshold for the lowest threshold fibers in each nerve. Somatic nerve-induced inhibition of spontaneous neuron activity without prior excitation was also observed. These results suggest that neurons of the solitary tract nuclei receive Group II and Group III somatic afferents which converge on neurons also receiving excitatory vagal input. Consequently, somesthetic and kinesthetic as well as visceral receptor activation may directly modulate solitary tract neurons. A possible conclusion is that the nucleus tractus solitarius is the initial central site of mediation of somatosympathetic reflexes. Modulation of the nucleus tractus solitarius by somatic afferents may then adjust sympathetic tone, via modulation of other medullary centers, in visceral and somatic tissues to match somatic metabolic needs.

Somatosympathetic reflex unilateral sweating and pupillary dilatation in a paraplegic man

Sympathetic spinal reflex responses to painful stimuli have been studied in experimental animals, but have rarely been demonstrated in human beings. We report the case of a paraplegic man with a high thoracic sensory level to pain, who developed unilateral pupillodilatation and sweating from the head to the midthoracic region as a response to rib fractures below the sensory level. This regional sympathetic reflex response was similar in many ways to that seen in spinally transected animals. Regional sympathetic reflex responses may provide a clinically useful sign of a painful and perhaps dangerous condition which is located below the analgesic level in spinal cord-injured patients.

Reflex responses evoked in the adrenal sympathetic nerve to electrical stimulation of somatic afferent nerves in the rat

The present study was initiated to determine the role of somatic A (myelinated) and C (unmyelinated) afferent fibers in both responses of increases and decreases in adrenal sympathetic nerve activities during repetitive mechanical pinching and brushing stimulations of the skin in anesthetized rats with central nervous system (CNS) intact. Accordingly, changes in adrenal sympathetic nerve activity resulting from repetitive and single shock electrical stimulation of various spinal afferent nerves, especially the 13th thoracic (Th13) spinal nerve and the sural nerve, were examined in urethane/chloralose-anesthetized rats. Repetitive electrical stimulation of A afferent fibers in Th13 spinal or sural nerve decreased the adrenal nerve activity similarly as brushing stimulation of skin of the lower chest or hindlimb did, while repetitive stimulation of A plus C afferent fibers of those nerves increased the adrenal nerve activity as pinching stimulation of those skins did. Single shock stimulation of spinal afferent nerves evoked various reflex components in the adrenal nerve: an initial depression of spontaneous activity (the early depression); the following reflex discharge due to activation of A afferent fibers (the A-reflex); a subsequent reflex discharge due to activation of C afferent fibers (the C-reflex); and following post-excitatory depressions. These reflexes seem to be mediated mainly via supraspinal pathways since they were abolished by spinal transection at the C1-2 level. Although the supraspinal A- and C-reflexes could be elicited from stimulation of a wide variety of spinal segmental afferent levels, the early depression was more prominent when afferents at spinal segments closer to the level of adrenal nerve outflow were excited. It is suggested that the decreased responses of the adrenal nerve during repetitive electrical stimulation of A afferent nerve fibers are attributable to summation of both the early depression and post-excitatory depression evoked by single shock stimulation, while the increased responses during repetitive stimulation of A plus C afferent fibers are attributable to summation of the C-reflex after single shock stimulation. In spinalized rats, repetitive stimulation of Th13 always increased the adrenal nerve activities regardless of whether A fibers alone or A plus C fibers were stimulated, just as brushing and pinching of the lower chest skin always increased them. The increased responses in spinal animals seem to be related to the fact that single electrical stimuli of Th13 produced A- and C-reflexes of spinal origin without clear depressions.

An intracellular study of the synaptic input to sympathetic preganglionic neurones of the third thoracic segment of the cat

In chloralose anaesthetized, paralyzed and artificially ventilated cats intracellular recordings were obtained from sympathetic preganglionic neurones (SPN) of the third thoracic segment of the spinal cord identified by antidromic stimulation of the white ramus T3. The synaptic input to SPNs was assessed, in cats with intact neuraxis or spinalized at C3, by electrical stimulation of segmental afferent fibres in intercostal nerves and white rami of adjacent thoracic segments and by stimulation of the ipsi- and contralateral dorsolateral funiculus and of the dorsal root entry zone of the cervical spinal cord. In both preparations SPNs showed on-going synaptic activity which predominantly consisted of excitatory post-synaptic potentials (EPSPs). Inhibitory post-synaptic potentials (IPSPs) were rarely observed. EPSPs were single step (5 mV) or, less frequently, large (up to 20 mV) summation EPSPs. The proportion of SPNs showing very low levels of on-going activity was markedly higher in spinal than in intact cats. Stimulation of somatic and sympathetic afferent fibres evoked early EPSPs (amplitude 3 mV, latency 5-22.3 ms), and late, summation EPSPs (amplitude up to 20 mV, latency 27-55 ms). Early and late EPSPs were evoked in nearly all SPNs in which this synaptic input was tested in the intact preparation (from 79-93% of the SPNs). In spinal cats, early EPSPs were evoked in 88% of the SPNs, whereas late EPSPs were recorded only in half of the neurones. No evidence for a monosynaptic pathway from these segmental afferent fibres to SPNs was obtained. In both intact and spinal cats, stimulation of the dorsolateral funiculus evoked early and late EPSPs in SPNs. Late EPSPs were recorded in 70% and 37% of the SPNs in intact and spinal cats, respectively. Early EPSPs, however, were evoked in all neurones. The early EPSPs evoked by stimulation of the dorsolateral funiculus had several components which are suggested to arise from stimulation of descending excitatory pathways with different conduction velocities. The following conduction velocities were calculated in intact (spinal) cats: 9.5-25 m/s (7.8-13.2 m/s), 5.7-9.5 m/s (5.5-7.8 m/s), 3.8-5.7 m/s (3.2-5.5 m/s), and 2.6-3.8 m/s (2.1-3.2 m/s). EPSPs of these various groups were elicited in a varying percentage in SPNs. EPSPs of the most rapidly conducting pathway were subthreshold for the generation of action potentials; some EPSPs of this group had a constant latency suggesting a monosynaptic pathway to SPNs. Stimulation of the dorsal root entry zone at the cervical level yielded essentially the same results as stimulation of the dorsolateral funiculus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of morphine on somatocardiac sympathetic reflexes in spinalized cats

The effects of morphine on sympathetic reflexes, recorded in the inferior cardiac nerve, to myelinated A and unmyelinated C afferent stimulation were tested in 17 acutely spinalized cats. Stable sympathetic A and C reflexes of short latency (approximately 30 ms and 140 ms in the case of the ulnar nerve, respectively) could be recorded in the inferior cardiac sympathetic nerve to stimulation of somatic A and C afferents in the ulnar and upper thoracic intercostal nerves, ipsilaterally. Spinal sympathetic A reflexes, which were primarily evoked from stimulation of A delta afferent fibers, could be elicited from more segmental levels than could sympathetic C reflexes. Additionally, smaller reflexes, only from A afferent fiber activation, were identified from stimulations on the contralateral side of the body. Small doses of morphine (0.02 mg kg-1, i.v.) proved to be ineffective at altering sympathetic A and C reflexes, while somewhat larger doses (0.2 mg kg-1, i.v.) produced a clear 62% decrease in C reflexes and a 33% decrease in A reflexes, Dosages of 1 and 2 mg kg-1 severely depressed both A and C reflexes. All of the above effects of morphine administration were completely and immediately reversible by naloxone (i.v.). The results are discussed with regard to the effects of morphine on sympathetic A and C reflexes in CNS intact, anesthetized cats.

The effects of vertebral artery injections of an enkephalin analogue, (D-Met2,Pro5)-enkephalinamide, on somatosympathetic reflexes

The present study was initiated to test the effects of intravertebral arterial injection of an enkephalin analogue (D-Met2,Pro5)-enkephalinamide on somatosympathetic responses to myelinated A afferent and to unmyelinated C afferent stimulation (A- and C-reflex, respectively). In anesthetized cats, 0.5 mg/kg administered directly into the vertebral artery, the artery supplying most of the cat brain stem and upper cervical spinal cord, depressed both the A- and C-reflex (to 66 and 64% of control, respectively) while intravenous or carotid arterial injections did not have any effect on these reflexes. It is suggested that intravertebral arterial administration may be a useful method of restricting the effective sites of delivery of biologically active compounds to areas of the brain supplied by this artery.

Depressive effect of morphine on the sympathetic reflex elicited by stimulation of unmyelinated hindlimb afferent nerve fibers in anesthetized cats

The effect of morphine on somatosympathetic reflexes was analyzed in central nervous system (CNS) intact, anesthetized cats. Sympathetic efferent nerve activity was recorded via an inferior cardiac nerve. Electrical train pulse stimulation of the superficial peroneal afferent nerve produced an A reflex of about 60 ms latency (evoked by myelinated fiber excitation) and a C reflex of about 360 ms latency (evoked by unmyelinated fiber excitation), both of which have central reflex pathways through the medulla oblongata. An intravenous injection of morphine (2 mg/kg), while not affecting the A reflex, markedly depressed the C reflex. The degree of this depressive effect was somewhat dependent on the stimulus intensity applied to the somatic afferent nerves. Naloxone (0.2 mg/kg, i.v.) antagonized the depressive effects of morphine on the C reflex. The present results suggest that the somatosympathetic C reflex can be a useful indicator of central morphine effects in anesthetized animals.

Monoamine release from cat spinal cord by somatic stimuli: an intrinsic modulatory system

1. Superfusates taken from spinal cords of cats anaesthetized with chloralose and urethane were assayed for endogenous serotonin and noradrenaline by high-pressure liquid chromatography with electrochemical detection. 2. Stimulating the dorsolateral funiculus, caudal to a spinal transection, enhanced in a frequency-dependent manner the levels of monoamines in the spinal superfusate. 3. Tyramine added to the superfusate enhanced the release of noradrenaline and serotonin. 4. In cats with intact neuraxes, stimulation of the sciatic nerve at high, but not low intensities produced a 2- to 3-fold increase in the levels of monoamines in the spinal superfusate. This evoked monoamine efflux was attenuated by cold block of the cervical spinal cord. 5. Stimulation of the infraorbital branch of the trigeminal nerve evoked the release of noradrenaline and serotonin from the lumbar cord in animals with intact neuraxes. Cold block of the cervical cord blocked trigeminal-evoked release of lumbar serotonin and noradrenaline. 6. That the monoamine efflux was not due to elevations in blood pressure was indicated by the failure of vasoxyl, an alpha-agonist producing hypertension, to evoke any changes in spinal monoamine levels. 7. The monoamine release was not dependent upon either an opiate-sensitive link or upon the activation of the sympathetic ganglia, because systemic administration of naloxone (an opiate antagonist) and chlorisondamine (a ganglionic blocking agent) failed to antagonize the evoked release of amines. 8. These results suggest the existence of a spinopetal monoamine system which is activated by peripheral stimuli. The modulatory influence associated with increasing monoamine tone in the spinal cord clearly indicated that somatic stimuli may activate a descending monoamine pathway which serves to modulate the magnitude of the ascending sensory message.

Somatosplanchnic reflex discharges in rats

Splanchnic efferent reflex discharges caused by electrical stimulation of limb afferent nerves or intercostal afferent nerves were studied in chloralose-urethane anesthetized rats. Stimulation of the limb afferent nerve produced late supraspinal reflex discharges via group II and III afferent excitation. Stimulation of the intercostal afferent nerve produced early spinal reflex discharges via group II and III afferent excitation and also late spinal reflex discharges via group IV afferent excitation. Intercostal afferent nerve stimulation seemed to strongly depress the splanchnic late supraspinal reflex discharges.

Electrophysiological characteristics of renorenal reflexes in the cat

1. Experiments were done in anaesthetized, paralysed and artificially ventilated cats to determine the fibre composition of renal nerves and to study the functional characteristics of reflex responses recorded in efferent renal nerves during electrical stimulation of contralateral and ipsilateral afferent renal nerves. 2. Renal nerves were found to contain three afferent fibre groups (Abeta, Adelta and C); the majority of these fibres reach the sympathetic chain through the least splanchnic nerve. Efferent sympathetic nerves to the kidney were found to originate from the greater, lesser and least splanchnic nerves through a synapse in the coeliac ganglion. 3. Two contralateral renorenal reflex responses were demonstrated during selective stimulation of renal afferent A and C fibres. The first (A renorenal reflex) was elicited by stimulation with trains of pulses at low voltage and high frequency (200 Hz), had an onset latency of approximately 100 msec and was followed by post-excitatory depression. The second (C renorenal reflex) was demonstrated by trains of pulses at high voltage and low frequency (20--30 Hz), had an onset latency of approximately 350 msec and was also followed by post-excitatory depression. 4. Ipsilateral renorenal reflexes with characteristics similar to the contralateral reflexes were also demonstrated. 5. Renorenal reflexes were abolished by destruction of the spinal cord and administration of nicotine sulphate (5--20 mg/kg, i.v.), but were not affected by bicuculline (0.4 mg/kg, i.f.). 6. The significance and the physiological role of these renorenal reflexes as well as their pathways within the central nervous system remain to be determined.